Conventional radiometric or colorimetric sensor systems employ either spectrally selective or nonselective photodetectors to quantify the luminance level of the light that reaches them. Such sensor systems have been used to calibrate Cathode Ray Tube (CRT) displays. To ensure accuracy, these sensor systems must maintain the sensor elements in contact with or at a uniform fixed distance from the display. A common implementation of such a sensor system utilizes a suction cup in order to firmly adhere the sensor to the CRT screen that has the additional effect of blocking out any ambient light from the sensor. For Liquid Crystal Displays (LCDs), however, the colorimetry of the display is dependent in part on the optical path length of the display which is the product of the birefringence of the liquid crystal material and the cell gap spacing. Since the glass of a LCD panel is relatively thin when compared to that of a CRT, the force of the suction used to attach that type of sensor would cause spacing changes that would change the luminous intensity of the light in that area and corrupt the accuracy of the very measurement that such a sensor would be attempting to make.
Unlike CRTs, both the luminance and the wavelength of light emitted from LCD flat panels vary depending on the angle at which they are measured or collected. This poses a problem for traditional color calibration sensors that all assume any portion of the light measured is representative of the whole. Therefore, it is desirable to provide a sensor system capable of accurately calibrating LCD devices that does not alter the cell gap spacing and collects luminance information orthogonal to the surface of the glass and with a narrow acceptance angle.